How do you pay with cash on the internet? You need some sort of card.

Gift cards purchased with cash.

You purchase a prepaid debit card with cash.

In a store with cameras.

is it that different from buying bitcoins by meeting physically with someone and paying cash? or do you buy bitcoins from your personal computer? I guess no way will be truly anonymous

I have read about people buying bitcoins by sending cash through the mail. That is perhaps the most anonymous one can get.

The seller has your mailing address. Mining is probably the most anonymous way to do it, and by far the least cost-effective. There are, however, ways to launder your bitcoins if you really want them to be anonymous, regardless of how you acquired them.

You can mine another cryptocurrency with your GPU and use that to convert to BTC. That's actually mildly profitable if you choose the right currency and your electricity costs are not too high.

If you are buying bitcoin, all you need is the seller's (seller of bitcoin) address to send the cash to.

I mean, imagine you go in with a baseball cap, and you go to a store that's nowhere near where you live. Is anyone really gonna be able to pull that up and ID you in 6 months? A year?

I use a scanner.

Sometimes, just a cell-phone camera.

Most e-commerce stores have access to a printer.